High-frequency antenna



April 19, 19 9 J. B. CA AVVAY, JR, Em 2, 67,9 2

HIGH-FREQUENCY ANTENNA Filed Jan. 28, -1947 Patented Apr. 19, 1949 UNITED STATES PATENT OFFICE HIGH-FREQUENCY ANTENNA Application January 28, 1947, Serial No. 724,746

Claims.

This invention relates to an improved antenna system for use in high frequency signaling, and is particularly concerned with high frequency antennae for the transmission of signals at a high energy level.

Much of the difficulty encountered in the operation of high powered, high frequency transmitting stations can be traced to the failure of insulation employed in the matching systems, coaxial lines, and other equipment associated with the antenna, and used in the construction of the antenna itself. These and other difliculties and obstacles are minimized in the present invention by eliminating the need for insulation in the antenna structure, the component elements of the antenna being secured rigidly together by conducting connections, serving both as structural supports for the radiating elements and as leads for feeding signal energy to such elements. These and other desirable results may be achieved without sacrifice of the effectiveness of the antenna as regards vertical directivity and uniformity of field strength in a horizontal plane. Thus the invention, in its broader aspect, may be applied to many systems of transmission which are recognized as highly efiicient for radiation of horizontally polarized energy, but which are difiicult to maintain because of structural weakness or inadequate insulation.

In the preferred embodiment of the invention, the radiating elements or members are supported on a hollow mast which embraces an inner conductor, the mast and conductor functioning as a coaxial line for the transmission of signal ener gy to the radiating members. The mast may be grounded at its base and electrically connected to the inner conductor at its upper end to provide a sturdy structure, and the diameter of the mast may be selected to afford requisite strength and adequate spacing from the inner conductor for the transmission of Rigid conducting elements, serving as structural supports, are used to connect the radiating members to the mast and the inner conductor respectively, whereby mounting of the radiating elements on the mast and positioning the inner conductor within the mast may both be achieved without the aid of insulation and with resultant increase in the rigidity of the structure. The simplicity, economy, and efficiency of such an arrangement are at once apparent.

It is, therefore, an object of the invention to provide an antenna system employing a hollow mast-,acting as the outer conductor of a coaxial transmission line, as a support for one or more iii igh voltage energy.

radiating members, such members being connccted both to the mast and to a conductor within the mast by rigid conducting elements, whereby the mast, inner conductor, and radiating members are structurally and electrically united and form a rigid unit, devoid of insulation.

Further objects and featuresof the invention will'appear from the following description, taken in connection with the accompanying drawings, in which Figure 1 is a vertical sectionalview of an antenna system, illustrating a preferred embodiment of the invention, and

Figure 2 is a horizontal section taken substantially on the line 2-2 of Figure 1.

In order to facilitate an understanding of the invention, reference is made to the form chosen for illustration, and specific language is used to describe the same. It will, nevertheless, be understood that no limitation of the scope of the invention or of its mode of application is thereby intended, such further forms and modifications being contemplated as would normally occur to those skilled in the art.

As shown in the drawing, the mast 4 is a hollow, tubular member, the dimensions of which are chosen to afford. adequate mechanical strength and sufficient spacing from the central conductor 5 to insure against leakage at high voltages. For instance, the internal diameter of the mast may be of the order of 6 inches when used with an inner conductor of 4 inch tubing. The height may vary considerably, but will be sufficient to accommodate the desired number of vertically spaced radiating members. As hereinbefore mentioned, conductor 5 and mast 4 are electrically connected at the upper end, for instance by welding conductor 5 to the central portion of cap 6 which serves as a closure for the upper end of the mast. While the mast, or the central conductor, or both, may extend higher, it will be appreciated, that such extension is wholly unnecessary to the practice of the invention; in any event, it may beconsidered that the electrical connection aforesaid is made at the efiective upper end of the two conducting memhere. The central conductor may be rigid, but this is not essential, the spacing between the conductors being maintained by the conductive connections to the radiating members, as hereinafter explained.

For the purpose of illustrating the invention, we have chosen radiating members constructed as described and claimed moreparticularly in the application for U. stLetters'Patent of John B.

Caraway, Jr. and Harvey Kees, Serial No. 648,- 840, filed February 20, 1946, the structure and function thereof being especially suitable in the practice of the instant invention. It will be ap preciated, however, that many advantages of the invention may be realized by the use of dipoles and other types of radiating members differing markedly in structure and function from the preferred type, and that such use is contemplated herein.

The nature of the preferred radiating members is shown more clearly in Figure 2. Thus each member consists essentially of an interrupted loop having a reactive element between the ends thereof. The loop, indicated at [0, may define a circular, hexagonal, or other plane figure; it may be formed by bending a single piece of conducting rod, pipe or tubing, for instance brass or copper, or by brazing, welding, or soldering together a plurality of sections.

The loop is interrupted at one side to provide a gap ll between the adjacent ends of the loop, and the gap is bridged by a reactive coupling as hereinbefore explained, preferably of the capacitative type. A convenient method of effecting this coupling is illustrated in the drawing, opposing plates I2 of a condenser being mounted on the respective ends of the loope for relative adjustment toward and away from each other, whereby the capacity may be varied to promote uniform current flow about the loop, thereby providing a substantially circular radiation pattern. Each plate I2 may be secured to the end of a stud I l having threaded connection with the loop structure, set screws being provided to prevent unintentional displacement of the threaded connection following adjustment to establish the necessary capacity.

At its opposite side the loop is rigidly secured to a supporting member 29, for instance by brazing or welding, as shown at 2 i. Supporting member 26, also conducting, may be similarly secured to the mast :3, the loop being thereby rigidly mounted on and electrically connected to the mast.

Adjacent the supporting member 29, the mast 4 is apertured to permit a conducting element secured to the inner conductor 5 and to the loop [0, to extend freely through the mast. Element 36 is sufiiciently rigid to serve as a structural element, uniting the rigidly mounted loop with the inner conductor 5, and thereby positioning and spacing the latter within the mast, as hereinbefore explained.

The position of the point of connection of element with loop l0, indicated at 32, will vary depending upon the characteristics of the system, and especially upon the resistance of the coaxial transmission line. The optimum location is that which gives the best standing wave ratio on the line below the lowermost loop when the line is fed by a signal of the frequency to which each loop has been adjusted by tuning its condenser l2. Increase in the number of radiating members mounted on the mast will, of course, require adjustment of the position of point 32.

The number of loops employed may vary widely; as is well known, the employment of a greater number of radiating members of this character increases the gain of the antenna system. A valuable feature of the invention resides in the feasibility of employing any desired number of loops, either odd or even. The uppermost loop shouldbe located below the upper end of the mast by a distance approximately onefourth wave length of the signal to be radiated, or

an odd multiple thereof, or by a commensurate electrical spacing (approximately degrees) offering no shunting effect to the transmission line. The spacing between adjacent loops in the ordinary case will preferably approximate the wave length of the radiated energy, the electrical spacing (usually about 360 degrees) being determined by the propagation velocity of the inner conductor. The principles underlying these various relationships are well known in the art and need no elaboration.

It will be appreciated that the spacing of the loops may be halved by reversing the phase relation of adjacent loops, for instance by locating point 32 on alternate loops at opposite sides of supporting member 2!! (but at the same distance therefrom). This has the effect of improving the radiation pattern.

The signal generator is connected to the system at the proper impedance to assure satisfactory operation, usually through a coaxial transmission line. It is often feasible to extend the mast, by the use of suitable pipe sections and couplings, to the generator, the inner conductor 5 being correspondingly extended, so that the use of a conventional coaxial cable for transmitting the signal to the antenna may be dispensed with. Where this is not possible, the mast is equipped at or near its lower end with a fitting to which a coaxial cable, extending from the generator, may be coupled. The shape of the mast will be determined largely by structural considerations; for instance, the mast may be tapered or otherwise reduced in size and weight toward its upper end in accordance with the usual mechanical principles.

The invention is particularly suited to high power, high frequency transmission of signal energy, and finds its principal use in this field. I Application of the invention to signal reception is also advantageous, however, and such use is intended to be covered hereby.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a high frequency antenna system, the combination with a hollow supporting mast grounded at its lower end and forming the outer conductor of a coaxial transmission line, of an inner conductor extending within said mast through the lower portion thereof and electrically connected to said mast at the upper end thereof, a plurality of radiating members, each comprising an interrupted loop having a reactive coupling between the ends thereof, mounted on said mast in vertically spaced relation, the uppermost radiating member being spaced from the upper end of said mast by a distance approximating onefourth of the wave length of the radiated signal, a rigid conducting support extending between said mast and each of said members and constituting the sole support for such member on said mast, and conducting means extending between said inner conductor and each of said radiating members, connected to each member at a point so spaced from the point of connectionof such member to said conducting support as to match the impedance of the transmission line below the lowermost loop, and being sufficiently rigid to main tain said inner conductor in position within said mast and in spaced relation therewith, said mast being apertured for free passage of said conducting means therethrough, whereby said mast, in-' net conductor, and radiating members are main- O tained in predetermined spaced relation solely by the conducting connections therebetween.

2. In a high frequency antenna system, the combination with a hollow supporting mast grounded at its lower end, of an inner conductor within said mast, said conductor being electrically connected to said mast at the upper end thereof, said mast and conductor forming a coaxial transmission line, a plurality of radiating members, each comprising an interrupted loop having a reactive coupling between the ends thereof, mounted on said mast in vertically spaced relation, a rigid conducting support extending between said mast and each of said members and constituting the sole support for such member on said mast, and conducting means extending between said inner conductor and each of said radiating mem bers, connected to each member at a point so spaced from the point of connection of such member to said conducting support as to match the impedance of the transmission line below the lowermost loop, and being sufliciently rigid to main-- tain said inner conductor in position within said mast and in spaced relation therewith, said mast being apertured for free passage of said conducting means therethrough, whereby said mast, inner conductor, and radiating members are maintained in predetermined spaced relation solely by the conducting connections therebetween.

3. In a high frequency antenna system, the combination with a hollow supporting mast grounded at its lower end and forming the outer conductor of a coaxial transmission line, of an inner conductor extending within said mast through the lower portion thereof and electrically connected to said mast at the upper end thereof, a plurality of radiating members, each comprising an interrupted loop having a reactive coupling between the ends thereof, mounted on said mast in vertically spaced relation, the distance between adjacent members affording an electrical spacing of about 360 degrees, the uppermost radiating member being spaced from the upper end of said mast by a distance affording an electrical spacing of about 90 degrees, a rigid conducting support extending between said mast and each of said radiating members, and conducting means extending between said inner conductor and each of said radiating members, and connected to each member at a, point so spaced from the point of connection of such member to said conducting support as to match the impedance of the transmission line.

4. In a high frequency antenna system, the combination with a hollow supporting mast forming the outer conductor of a coaxial transmission line, of an inner conductor within said mast, said inner conductor being electrically connected to said mast at the upper end thereof, a plurality of radiating members mounted on said mast in vertically spaced relation, a rigid conducting support extending between said mast and each of said members and constituting the sole support for such member on said mast, and conducting means extending between said inner conductor and each of said radiating members, connected to each member at a point spaced from the point of connection of such member to said conduc ing support, and being sufficiently rigid to maintain said inner conductor in position within said mast and in spaced relation therewith, said mast being apertured for free passage of said conducing means therethrough, whereby said mast, inner conductor, and radiating members are maintained in predetermined spaced relation solely by the conducting connections therebetween.

5. In a high frequency antenna system, the combination with a hollow supporting mast forming the outer conductor of a coaxial transmission line, said mast being grounded adjacent the lower end thereof, of an inner conductor within said mast, said inner conductor being electrically connected to said mast at the upper end thereof, a plurality of radiating members mounted on said mast in vertically spaced relation, the uppermost of said members being spaced from the upper end of said mast by approximately electrical de-v grees, a rigid conducting support extending between said mast and each of said members and constituting the sole support for such member on said mast, and conducting means extending between said inner conductor and each of said radiating members, connected to each member at a point spaced from the point of connection of such member to said conducting support, and being sufficiently rigid to maintain said inner conductor in position within said mast and in spaced relation therewith, said mast being apertured for free passage of said conducting means there through, whereby said mast, inner conductor, and radiating members are maintained in predetermined spaced relation solely by the conducting connections therebetween.

JOHN B. CARAWAY, JR.

ROBERT M. SILLIMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,153,768 Morrison Apr. 11, 1939 2,289,856 Alford July 14, 1942 2,298,449 Bailey Oct. 13, 1942' 2,321,454 Brown June 8, 1943 2,324,462 Leeds July 13, 1943 2,405,123 Fyler Aug. 6, 1946 2,431,124 Kees Nov. 18, 1947 

